For example, Patent Literature 1 discloses, as technology on electric boosters, a vehicle brake system including a brake assist device which boosts a brake pedal effort by a motor being driven, and a stroke detection device which detects a movement position of an input rod on the basis of a brake pedal operation amount. In this vehicle brake system, the hydraulic pressure of brake fluid is controlled by the brake assist device to feed the brake fluid to a hydraulic control unit on the basis of the brake pedal operation amount detected by the stroke detection device.